Input/output unit switch



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I R AR 1 READ BUS P TU-O READ BUS P TC-A Q READ BUS 0 TU 0 READ BUS 2TC-A READ BUS 2 ru-o READ BUS 5 TU-O READ BUS 5 TC-A E READ BUS 4 TU-O vREAD BUS 5 TU-O READ BUS 5 TH RLY READ BUS s TU-O READ BUS 0 TH WRITEECHO Tu-D WRITE ECHO TC-A READ BUS 7 TU-O A 86 READ BUS P TU-T A L READBUS D TU-7 READ BUS 1 TC-A RLY READ BUS 1 READ BUS 7 TC-A READ BUS 2 8READ BUS 5 TU-Y READ BUS 4 TU-Y READ BUS 4 TH READ BUS 5 TU-7 READ BUS 6TCA RLY WR'TE ECHO READ BUS 6 TU-Y READ BUS 7 TU-Y A7, LO. Q AR UnitedStates Patent ()fiice 3 ,372,378 Patented Mar. 5, 1968 3,372,378INPUT/OUTPUT UNIT SWITCH Ernest W. Devore, Poughlreepsie, Roy J. Smith,Wappingers Falls, and John M. Tyrrell, Hyde Park, N.Y., assignors toInternational Business Machines Corporation, New York, N.Y., acorporation of New York Filed Apr. 27, 1964, Ser. No. 362,710 21 Claims.(Cl. 340-1725) ABSTRACT OF THE DISCLOSURE An input/output (I/O) unitswitch operated by a plurality of control units, permitting them toindependently select and use any available I/O unit from a plurality ofI/O units. No additional computer instruction is needed to recognize theexistence of the I/O unit switch, which is a passive device thatresponds to standard I/O select instructions needed without the I/Oswitch. Coordinating selection circuitry prevents improper selection ofany I/O unit. A modular configuration with nodes having slow speed(relay) bus switching circuits and high speed (semiconductor) controlcircuits permits full performance in switching and controlling magnetictape units. The control units may be connected to the same or dilferentcomputer systems.

This invention relates generally to a switching system for selectivelyconnecting any input/output (I/O) unit of a plurality of I/O units toany control unit of a plurality of control units. All control units cansimultaneously operate with different I/O units. Furthermore, any I/Ounit can be permanently made not available to any control unit on aselective basis.

The commonest means of selecting an I/O unit from a group of units isvia a direct connection between a control unit and each of a pluralityof I/O units. In this sense, a control unit is designed to accommodateup toa specific maximum number of I/O units.

Tape units are a form of I/O unit and hereafter are used to representI/O units generally. Frequently, it is desired to increase the capacityof a magnetic tape unit installation without the use of specialapparatus through the use of additional tape controls. In this case,each tape control selects among only its own bank of tape units, and itcannot operate tape units connected to other tape controls.

For example, an overall computer installation may have two tape controlsand 16 tape units, in which 8 of the tape units are connected to onecontrol unit while the remaining 8 tape units are connected to theremaining control unit. One tape control can operate only with one ofits 8 tape units and cannot operate with the 8 tape units connected tothe other control. In this event, the addition of a tape control and itstape units does not increase the flexibility of either the tape controlsor the individual tape units, although it increases the I/O capacity ofthe system due to the addition of more units. It is, therefore,desirable to be able to find a convenient means of increasing theflexibility of an installation so that any of several tape controls canoperate with any tape unit among all tape units at an installation. Amethod of accomplishing this end is a tape unit switch (TUS). The tapeunit switch connects between a plurality of the tape controls and aplurality of tape units so that any of the plurality of tape units isselectable by any of a plurality of tape controls.

Various tape unit switches have been suggested, some of which aredirectly address programmable and require special instructions by thecomputing system in order to connect a given tape unit to a given tapecontrol. Other tape unit switches are manually controlled to connect aparticular tape unit to a particular tape control. The manual switchoffers the flexibility of changing a semipermanent tape unit connection,but it cannot provide tape switching between data block transfers by acomputer system without first stopping the system, which is highlyundesirable.

It is an object of the invention to provide switching means to allow anyof a plurality of control units to be connected selectively to any of aplurality of I/O units. In some cases, the total number of available I/Ounits can exceed the maximum number that can normally be attached to :acontrol unit.

It is an other object of the invention to provide an I/O switch whichcan operate without the necessity of any special computer instruction orany other special program intervention by a computing system, and yetcan operate under complete computer control.

It is a further object of this invention to provide an I/O unit switchhaving the general physical configuration of a two-dimensional matrix.

It is another object of this invention to provide a switch that canoperate all input-output lines between a control and its selected I/Ounit.

It is a further object of this invention to provide switching circuitrythat allows an overlapped operation between a high speed tape controlunit and a relatively slow I/O unit by overlapping data bus switchingwith read or write delays of an I/O unit.

It is still another object of this invention to provide means forlocking out the availability of a particular I/O unit to any one or morecontrol units.

It is another object of this invention to provide an I/O switch capableof modular expansion for future increase in the number of I/O units and/or controls in a computer installation.

It is object of this invention to provide an I/O switch between pluralI/O units and plural controls, where the controls can be connected todifferent channels of the same computer system, or to channels ofdilferent computer systems, or to channels of a computer system and tooft-line devices.

It is another object of this invention to prevent another control frominterfering with the operation of an I/O unit once the I/O unit has beenselected by any control.

It is an object of this invention to permit any control to sample thestatus or type of any I/O unit connected to an I/O switch, even thoughthe I/O unit is being operated by another control.

It is another object of this invention to permit an I/O selectinstruction from a computer to any of its tape controls to select amongany available tape unit in the computer installation.

It is a further object of this invention to provide a pluralcontrol-plural tape unit switch capable of switching among its tapeunits between normal data block transfers to or from a computer with noloss of time in system operation due to switching, compared to the timerequired to switch between tape units on a single tape control nothaving a tape unit switch.

The foregoing and other objects, features and advantages of theinvention will be apparent from the follow-

